Halo: MCC co-op -- Mission Progress not saving?

I know Halo: MCC has had a slew of bugs since launch. My brother and I, both new to Halo entirely, bought the game on launch day with the hopes of playing through all of the campaigns together via online co-op play. We thought the bugs were mostly tied to competitive online multiplayer matchmaking, but we tried to connect the first week for co-op (just the two of us) but couldn't, so we decided to just wait a few weeks till patches came through.

However, this past weekend we were able to meet up in person and tried to play local co-op together. I signed into my account, booted up Halo: MCC and went to the Halo 1 campaign, added him to my roster via the X button, then we both played the first 3 missions together. We chose to "save and quit" and then went to bed. The next day we came back to continue our progress and found that progress said 0/10 missions complete and that if we play co-op it will revert back to the start of the mission (as opposed to a mid-mission checkpoint, I presume). We were supposed to be on Mission 3 so we said yes, but, to our dismay, it started us out on Mission1. So, we thought, "well, maybe we didn't save it properly last night?" and we tried again, this time beating Mission 1 again. We finished that mission and then chose to "save and quit" again and closed the game and re-opened it again and it still said Mission progress was 0/10.

What gives? Is this a known bug? (Xbox Support isn't answering me, so I'm not sure), or are we doing something wrong? I presumed we could both progress through the game together, even switching back and forth between local co-op and online co-op, without issue? I realize all the levels are unlocked from the start, but I think we cannot earn the achievements related to beating the game on Normal / Heroic / Legendary modes, etc without that mission progress saving.

As far as the "missions complete" issue, I've seen this happen a couple of times, but not limited to co-op missions. Very annoying.

Mid-mission save points with co-op has always been this way (from the original Halo on xbox). Not sure why, but Halo never saves your progress mid-mission when in co-op. You'll have to complete the whole mission in one sitting and then hope TMCC marks it as "completed".

As far as the "missions complete" issue, I've seen this happen a couple of times, but not limited to co-op missions. Very annoying.

Mid-mission save points with co-op has always been this way (from the original Halo on xbox). Not sure why, but Halo never saves your progress mid-mission when in co-op. You'll have to complete the whole mission in one sitting and then hope TMCC marks it as "completed".

I contacted Xbox Support and they had me 1. power cycle, 2. clear persistent storage, 3. clear MAC Address. My brother and I both did it. Interesting, the mission progress thereafter unlocked on his account (the console we were both signed into), but not on my account/console. My brother and I then played online co-op and it saved our mission progress. The next day, I went back and played local co-op with my wife on my own console and it again did not count my mission progression. I'm getting really sick of beating The Pillar of Autumn on Halo: CE (><)